Referring to FIGS. 14A to 17C, embodiments of the conventional electron tube, for example, the conventional display device will be described. Like reference numerals in FIGS. 14A to 17C represent like parts.
There are shown in FIGS. 14A and 14B a partial top view of a first prior art fluorescent display device and a cross sectional view taken along a line X1—X1 of FIG. 14A, respectively.
As shown, the first prior art display device includes a glass substrate 51, a pair of metallic plates 52, 53 formed on the glass substrate 51, an anchor 54 and a support 55 which are respectively installed at the metallic plates 52, 53 via a pair of mounting portions 541, 551 thereof, and a cathode filament 56. Referring to FIG. 14B, one end of the filament 56 is fixed to the anchor 54 and the other end thereof is fixed to the support 55. In this case, the anchor 54 acts as a resilient member for exerting the tension force on the filament 56 so that it will not hang down and the support 55 functions as a post for supporting the filament 56.
The fastening process of the filament 56 will now be described in detail.
One end of the filament 56 is interposed between a supporting portion of the anchor 54 and a metallic piece 5411, and then the metallic piece is fixed to the supporting portion by a resistance heating welding. The resistance heating welding is carried out by applying an electric current on a pair of heating electrodes (not shown) disposed at bottom of the supporting portion of the anchor 54 and top of the metallic piece. Similarly, the other end of the filament 56 is fixedly joined to the support 55.
When a driving system for applying DC voltage to the filament is employed, a potential gradient develops between the filament and an anode electrode (not shown), and the filament and a grid (not shown) due to a voltage drop of the filament. This induces differential in luminance of both ends of the filament.
Accordingly, in order to reduce influence of the potential gradient as shown in FIG. 15A, a second prior art display device including a plurality of sets of two filaments 661, 662 (one set shown) has been proposed. FIG. 15B illustrates a cross sectional view taken along a line X2—X2 of FIG. 15A. As shown, polarities of the two filaments 661, 662 are provided to be different from each other as will be described later.
The filaments 661, 662 are supported by a first set of an anchor 642 and a support 652 and a second set of another anchor 641 and another support 651, respectively. To be more specific, one filament, e.g., 662 has both ends fixed to a first set, one end to the anchor 641 and the other to the support 651, and the other filament 661 has both ends fixed to a second set, one end to the anchor 642 and the other to the support 652. The anchors 641, 642 are respectively mounted on a glass substrate 61 via their corresponding metallic plates 621, 622, and the supports 651, 652 are respectively mounted on the glass substrate 61 via their corresponding metallic plates 631, 632. Under this condition, a positive potential is applied to the metallic plates 621, 632 and a negative potential is applied to the metallic plates 622, 631.
There are shown in FIGS. 16A and 16B, a partial top view of a third prior art display device including linear spacers 851 (one shown), a damper 852 and filaments 86 (only one is designated by the reference numeral), and a cross sectional view taken along a line X3—X3 of FIG. 16A, respectively.
As shown, one end of the filament 86 is connected to a cathode electrode 82, and similarly the other thereof (not shown) is connected to another cathode electrode (not shown). The filament 86 has a predetermined vertical position sustained by the spacer 851 disposed near its one end and another spacer (not shown) disposed near its other end. The spacer 851 made of a metal line has both ends fixedly attached to spacer supports 831, 841. The spacer supports 831, 841 are fixedly mounted on a glass substrate 81 via an insulating layer 84. The damper 852 made of a metal line is installed between the spacers to prevent the filament 86 from coming into contact with other components mounted at the glass substrate 81. Similar to the spacer 851, the damper 852 has both ends fixed to a pair of damper supports 832, 842. In this prior art, the supports 831, 832 and 841, 842 are respectively corresponding to the anchor 54 and the support 55 shown in FIG. 14A according to the first prior art.
The fastening process of the damper 852 will now be described in detail.
Both ends of the damper 852 are respectively interposed between a supporting portion at the top of the support 832, 842 and a metallic piece 8321, 8421 of each of the damper supports 832, 842 and then the metallic pieces are welded to the supporting portion of its corresponding support by the resistance heating welding. The damper supports 832, 842 are fixedly attached to the anode substrate 81 by using a fritted glass. As above-mentioned, the resistance heating welding is carried out by applying current on a pair of heating electrodes disposed at bottom of the supporting portion and top of the metallic piece corresponding to each of the damper supports 832, 842.
Similarly, both ends of the spacer 851 are also joined to the supports 831, 841.
There are shown in FIGS. 17A to 17B, a partial top view of a fourth prior art display device including wire grids 71 (only one is designated by the reference numeral), and a cross sectional view taken along a line X4—X4 of FIG. 17A, respectively.
As shown, a reference numeral 701 represents an anode substrate made of a glass, a ceramic or the like; 702 a side plate made of, e.g., a glass; 71 wire grids (only one is designated by the reference numeral); 75 anode electrodes (only one is designated by the reference numeral); 761 cathode filaments (only one is designated by the reference numeral); and 762 a support for the cathode filament 761, respectively.
Referring to FIG. 17B, under the condition of applying a predetermined tension force to the wire grid 71 mounted on the jig (not shown), the wire grid 71 is mounted on the spacer 72 made of an insulating material. Next, one end 712 of the wire grid 71 is interposed between the anode substrate 701 and the side plate 702, and similarly the other end thereof is interposed between the anode substrate 701 and another side plate (not shown). Thereafter, the ends of the wire grid 71, the anode substrate 701 and the side plates are connected to each other by using the fritted glass.
Referring to FIG. 17C showing a cross sectional view of a modification of the display device of FIG. 17B, under the condition that the predetermined tension force is exerted on the wire grid 71, both ends of the wire grid 71 are fixedly attached to the spacer 72 by using the fritted glass. The wire grid 71 is connected to grid terminals 714 (one shown) via conductive members 713 (one shown).
In the first display device, the supporting member such as the anchor or the support is of a complicate shape due to the three-dimensional shapes, increasing factory expenses thereof and making a mounting process of the filament difficult. Additionally, the supporting members should have a predetermined strength, setting a limit on the miniaturization of the device. In other words, it is difficult to make the display device thin. Further, since the area for mounting the supporting member and the metallic plates is large, the space excepting for the display area, so-called dead space, is enlarged.
The second display device solves the potential gradient between the filament and the anode electrode and between the filament and the grid, but the mounting space for the supporting member and the metallic plates is about twice as much as that of the first prior art display device. That is, the spatial problem still remains.
Similar to the first display device, the supporting member such as the anchor or the support of the third display device is also of a complicate shape due to three-dimensional shapes, increasing factory expenses thereof and making a mounting process of the spacer and the damper difficult. Further, the supporting member should have a predetermined strength that in turn sets a limit on the miniaturization of the device. On the other hand, it is difficult to make the display device thin.
In the first and/or the third display device, when the filament or the damper is welded by using the resistance heating welding, the welding flames spark and the welding remnants due to the welding flames are attached to other components, deteriorating the display quality. For instance, in the case that the filament or the damper is welded, the welding flames may have direct contact with the fluorescent substance applied to the anode electrode, thereby being stuck thereto, or the welding remnants, which are attached to the anchor or the supporting member in the welding work, may get stripped off in the subsequent processes to be stuck to the fluorescent substance, making the poor display. Further, the welding remnants may develop a short-circuit between the electrodes. On the other hand, when the welding is performed, the portions excepting for the welding points are also heated. This results in the anchor and the supporting member or the like being expanded, developing cracks in the anode substrate.
The fluorescent radiation device such as the fluorescent display device is fabricated by installing the damper, the spacer or the wire grid and then performing the heating process several times. For example, the fritted glass is used for fixedly attaching the supporting member in the third prior art and the wire grid in the fourth prior art. Therefore, the heating temperature in the steps thereafter should be maintained at a lower level than the melting point of the fritted glass. However, it is cumbersome to maintain the foregoing temperature and sometimes the fritted glass is melted to deviate the initial positions of the members fixed thereby. Moreover, since the components constituting the display device should be made of the materials which can undergo the heating process at a temperature below the melting point of the fritted glass, the applicable materials are limited.